Second only to the Water Triple Point and in many ways, because of its ease of use and purity, superior to it, is the Gallium Melt Point. At 29.7646°C, this is a very convenient temperature, as it is the closest ITS-90 fixed point to ambient temperatures, and also close to human body temperatures, which are critical ranges for many industries.
Confidence is a major requirement in a standard. The Isotech Gallium Cell and Apparatus have a long history, and have been successfully used in most National and Primary Laboratories world-wide.
International comparisons prove the quality of the Isotech Cells, and we have a unique number and history of comprehensive evaluations.
Calibration of Isotech's Reference Cell with the Standard at NIST showed an agreement of 4μK, 0.000004°C.
The Isotech Gallium cells contain the highest purity metal, >99.99999% pure (7N), and giving a flat plateau. The cell has a day-to-day reproducibility of just +/-0.000025°C
Developed in the 1970s by Henry Sostman, the design is of the highest standard. The metal is contained within a resilient inner housing that ensures no contamination or reaction with the gallium. The surrounding outer metal sleeve provides longitudinal uniformity of temperature, and further mechanical strength. Of several hundred cells, shipped to all parts of the world, all have arrived without damage.
In general, we recommend the sealed cell. It has the convenience of the sealed construction, along with the sub mK performance.